Currently, cataract extraction is the most common ophthalmic surgical procedure performed in the United States. Approximately 400,000 lenses are removed every year. These lenses, however, must be replaced with a prosthetic optical device before useful vision can be restored to the operated eye. With the lens removed, light rays are no longer focused on the retina and vision is very poor without corrective glasses, contact lenses or an intraocular lens.
Corrective eye glasses have been the classic and most common method of correcting aphakia. Corrective glasses, however, being located in front of the normal position of the human lens, can produce magnification and distort the shape of viewed objects. Contact lenses cause less magnification and distortion, but very old and very young patients frequently find handling and wearing these small lenses difficult. With implanted intraocular lenses, there is little or no magnification or distortion and there is no need to remove the lens from the eye or otherwise handle the lens. Generally, the lenses provide good visual acuity at all times, even at night.
Intraocular lenses have definite advantages in terms of vision and convenience over the other methods of aphakic correction. While intraocular lenses have definite advantages over corrective glasses and contact lenses, intraocular lenses have specific disadvantages.
Intraocular lens implantation surgery is more traumatic than simple cataract extraction alone. The additional handling of the cornea and manipulation inside the anterior chamber during lens implantation add to the amount of trauma to the eye. There also are certain surgical dogma that must be adhered to. It is a cardinal rule in any surgery that the surgeon have good exposure. In implant surgery, however, the surgeon must have excellent exposure. Extreme care must be exercised to limit trauma to the cornea, structures of the anterior chamber, and other structures.
A large number of different types and styles of intraocular lenses has been developed. Major classes of lenses can be distinguished based on the method of fixation in the eye. Anterior chamber lenses lie entirely in front of the iris. Iris-supported lenses rely on the structural integrity of the iris to stabilize and support the lens within the eye. Capsule-fixated lenses are inserted into a planned extracapsular cataract extraction space between the anterior and posterior leaves of the lens capsule.
Anterior chamber lenses rely on haptics, also called feet or loops, propped against the scleral spur in the chamber angle to support and fix the lens in the eye. Lenses must be carefully designed with thin feet or haptics to prevent the feet from touching the corneal endothelium.
Iris-supported lenses, on the other hand, have an arrangement of struts, or loops, some anterior and others posterior to the iris. These struts or loops function like a clip. Other iris type supported lenses require the iris to be interwoven about alternating feet, and some iris-supported lenses have small haptics with holes therein for direct suturing to the iris.
With capsule-fixated lenses, a planned extracapsular cataract extraction is performed. The haptics of the lens are then inserted into the space between the anterior and posterior leaves of the capsule. This is referred to as the "in-the-back" technique. The haptic loops, however, often are positioned in the ciliary body sulcus between the ciliary body and the iris root. If performed properly, the capsule and any residual lens cortex adhere firmly to the lens, fixing it securely in place. Good capsular fixation is much more stable than iris fixation, and movement of the implant in the eye is reduced.
Common to all lens classes, particularly anterior chamber lenses and capsule-fixated lenses, is trauma associated with implanting the lens. That the lenses always have to be larger than the space provided for their implant in the eye is a principal cause of the trauma.
Implantation of currently used lenses in their proper position within the eye requires the reduction of lens size inside the eye during surgery. In this microfine surgery, the long, thin haptics or feet attached to thin lenses must be manipulated within the eye, often requiring uncommon agility on the part of even skilled surgeons. Space limitations in the eye, the required size of the lens once implanted and considerable manipulations of the lenses during implantation by the surgeon can result in traumatic damage to the corneal endothelium and very often rupture of the posterior capsule by the novice. Damage to the corneal endothelium and rupture of the posterior capsule are complications considered serious.
It would be expedient to offer an intraocular lens, for placement in either the anterior chamber or posterior segment, that could be implanted in a very nearly atraumatic manner.
It would be desirable if an intraocular lens were provided that during surgical implantation was small for easy insertion into the eye with minimum trauma to the cornea and other structures while later being easily made larger to effect a firm, secure fit in the eye. Such lenses could be implanted by relatively inexperienced implant surgeons without considerable manipulations of the lens during surgery. Damage to the corneal endothelium and rupture of the posterior capsule would occur less often, thus minimizing compromises to a patient's welfare.